Current estimates of fossil fuel supplies for the world's energy supply indicate that production will drop below consumption within 10 to 20 years. The availability of alternative energy sources that do not utilize fossil fuels such as hydroelectric, solar, wind, geothermal, tidal power can be expected to be increased. One currently available power source, that of nuclear fission reactors, could be relied upon, if needed. However, nuclear fission reactors have become very unpopular due to their risk and highly radioactive waste products.
One potential choice for future energy production, that has always been described favorably, is nuclear fusion. One benefit of fusion reactors is they do not rely on dangerous radioactive heavy elements, as do fission reactors. Other benefits include a nearly inexhaustible fuel supply coupled with a much smaller, approximately 1,000 times smaller, volume of waste products. While the fusion process does create some radioactive waste products, the volume is small, and the radioactivity is mild and short-lived compared to fission waste products. Fusion waste products are estimated to have half-lives of tens of years rather than the thousands of years for fission waste products. In summary, nuclear fusion reactors hold the promise of unlimited, essentially clean power. For a general background on nuclear fusion, reference is made to Lapedes, Encyclopedia of Energy (1976), and Wilhelmsson, Fusion: A Voyage Through the Plasma Universe (2000).
The problem is, other than in nuclear fusion bombs, scientists have been unable to get more energy out of a nuclear fusion reaction than has been used to start the reaction. In other words, nuclear fusion reactors, to date, have failed in the goal to produce energy because they consume more energy than they produce. Ultimately, the goal of nuclear fusion reactors is to create more power than is used to start the process.
The most important common problem in all past nuclear fusion reactor designs is the formation of instabilities in the plasma that have resulted in less than ideal burns. While many types of instabilities have been described in the past, a physical understanding of the cause of these instabilities has been elusive. The reactor designs of the current invention are in part based upon a new physical understanding of the cause of plasma instabilities, how they can be eliminated, and how they can be used when they do result.
The second most important problem in all past nuclear fusion reactor designs is the efficient creation of electrical power from the energy produced by the fusion reaction. Efficient conversion of extracted energy into electrical power is needed. Most designs have assumed the heat produced by the fusion process will be extracted to drive steam turbine and generator systems. Thermal transfer using the heat produced by the fusion process is not the most efficient manner of converting extracted energy into electrical power.
The third most important goal of nuclear fusion reactors is to create energy economically. This goal has not been achieved by prior designs because they failed to produce any net energy.
Many designs rely on pulses of fusion burns. In other words, the fusion process does not continuously burn for extended periods of time. To be economical, the fusion burns should last for extended periods of time.
Researchers have approached the problem of creating nuclear fusion reactors in a variety of ways. Perhaps the most fundamental element of the reactor design is the geometric shape of the reactor. The shape of the reactor is critical in all elements of the fusion process including ignition of the fusion reaction and confinement of the active plasma and its corresponding instabilities.
Inertial Confinement Fusion (ICF) is a method by which fusion has been initiated through an implosion reaction using lasers, neutral particle beams or ion particle beams. ICF reactor designs have succeeded in advancing fusion research by successfully reaching high temperatures and densities. While the shape of the confinement reactor in ICF designs has been generally spherical, the walls of a reactor chamber for current ICF designs are full of holes and apertures by which the lasers or particle beams are introduced and by which sensors and other instrumentations access the reactor chamber. The resulting chamber presents a very irregular and asymmetrical chamber for the containment of the fusion burn. Unlike other reactor designs, active electromagnetic containment fields are not utilized as part of the ICF design.
A number of reactor designs use toroidally-shaped (donut-shaped) confinement arrangements for the reactor, or variations on a toroidally-shaped reactor. These include:
Standard Tokamak Fusion: Tokamak fusion reactor designs contain the fusion fuel plasma in a toroidally-shaped electromagnetic containment field. These designs have been able to contain plasmas for extended periods of time, reach high temperatures and develop high densities.
Spherical Tokamak Fusion: The cross section of a normal Tokamak is circular. The cross-section of a “spherical” Tokamak is more elongated in the vertical direction.
Stellarators: In general, there is little difference between Tokamaks and Stellarators—they are both toroidal. The orbit of plasma in a Tokamak is planar—i.e., there is no vertical motion. The orbit of plasma in some Stellarator designs is non-planar—i.e., there is vertical motion.
Reversed-Field Pinch (RFP): Reversed-Field Pinch devices are similar to a Tokamak in that the plasma is confined by both toroidal and poloidal magnetic fields. The main difference is the relative strength of the magnetic fields.
Field Reversed Configuration (FRC): The Field Reversed Configuration is another toroidal system with magnetic field lines arranged differently.
Some of the earliest devices for creating high-temperature plasmas used cylindrical patterns. These designs included:
Theta Pinch: Theta Pinch designs take the form of a long tube or a skinny torus. The Theta Pinch uses an electrically induced magnetic field to compress and heat the plasma.
Mirror Machines: A Mirror Machine operates essentially like a Theta Pinch except a strong magnet is placed around each end of the tube in an attempt to deflect the plasma backwards towards the opposite end of the tube.
Z-pinch: The idea of the Z-Pinch, best embodied in Sandia National Laboratory's Z-Pinch device, is to suddenly apply a massive voltage across a cylindrical pattern of wires, causing the wires to vaporize. The cross-product of the Electric and Magnetic fields produced, described using the Poynting Vector, or classically as the Electromagnetic Momentum, of the induced fields, collapses the plasma in a cylindrical pattern.
MAGO: Russian researchers have developed a device called “MAGO.” This device passes a large electrical pulse through an approximately cylindrical copper chamber. The geometry of this device is not spherical. In the MAGO system a deuterium and tritium gas is placed in the approximately cylindrical copper chamber. Next, a massive electromagnetic pulse heats the gas to a plasma state. This gas then flows past an inner nozzle, further heating areas of the plasma.
An intermediate approach between magnetic confinement devices and inertial confinement devices called Magnetized Target Fusion (MTF) has been used by the military to study fusion bombs. In a MTF device, a “magnetized target plasma” is placed within a containment vessel and is explosively imploded. In essence, these devices are bombs. In one planned device by Los Alamos National Laboratory, Los Alamos documents describe potential plans to create a quasi-spherical compression by cylindrically compressing a spherically shaped liner.
Unfortunately, none of the aforementioned devices have accomplished the ultimate goal of extracting commercial energy through the use of nuclear fusion. There remains no viable design for a commercial fusion reactor. Accordingly, it would be desirable to provide a design for a nuclear fusion reactor system that could achieve this goal and overcome the problems encountered with existing designs.